The separation of enantiomers continues to be a considerable challenge in preparative chemistry, particularly on an industrial scale.
The majority of currently used methods for the resolution of racemic mixtures are based on the diastereomeric interactions of the individual enantiomers of the racemic mixture with an optically-active resolving agent. For instance, by chemically reacting a racemate with an optically-active resolving agent, a pair of diastereomers are produced which can be separated on the basis of their different physical properties. Rather than forming discrete compounds (diastereomers) from which the enantiomers must be recovered by subsequent chemical reactions, it is also possible to make use of diastereomeric complexes or reversible interactions to achieve resolutions. Such an approach forms the basis of chromatographic separations involving either the use of a chiral stationary phase or of a chiral additive to the mobile phase; see I. W. Wainer, Chromatography Forum, 1, 55 (1986).
Certain chiral functional homopolymers, e.g., poly(acrylo)-aminoacids, are useful as effective crystallization inhibitors of one enantiomer in the resolution of racemic mixtures that crystallize in the form of conglomerates; see U.S. Pat. No. 4,864,031. Chemical yields, however, are relatively low when high enantiomeric excesses are desired. Other optically-active functional polymers, including optically-active polymers bearing polar non-ionic oligoether groups or cationic quaternary ammonium groups, have been investigated by S. D'Antone et al., in Reactive Polymers, 3, (1985), pages 107-125.